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A.H.GREBE. RECEIVING APPARATUS FOR RADIO TRANSMISSION SYSTEMS.

APPLICATION FILED NOV. 2 I914- Patented Aug. 8, 1916.

I I I I N I I I 1 I I I I I I I l ATTORNEYS BY A ALFRED H. GREIBE, OF RICHMOND. HILL, NEW YORK, ASSIGNOR TO EUGENE F. MILLER,

' F RICHMOND HILL, NEYJ YORK.

RECEIVING APPARATUS FOR RADIO TRANSMISSION SYSTEMS.

Specification of Letters Patent.

Application filed November 2, 1914. Serial No. 869,783.

To all whom it may concern:

Be it known that I, ALFRED H. GREBE, a citizen of the United States, residing at and whose post-oilice address is No. Van Wyck avenue, Richmond Hill, county of Queens, State of New York, have invented certain new and useful Improvements in Receiving Apparatus for Radio Transmission Systems; and I do hereby declare the following to be afull, clear, and exact description of the invention, such as will en- 1 able others skilled in the art to which it appertains to make and use the same.

This invention relates to receiving apparatus for radio transmission systems. It is of special utility in a receiver for a wireless telegraph system although it may also be used in systems of Wireless telephony.

The invention is directed to the provision of a receiving apparatus which is of simple construction, which may be manufactured at low cost, which occupies but little space and with which the sounds of the received signals are amplied or intensified to such an extent that they may be heard at a distance from the receiving apparatus and without holding a portion of the apparatus to the ear.

In receiving apparatus for wireless telegraph systems, it has been common heretofore to utilize a telephone receiver connected in the receiving circuit and to hold this receiver close to the ear in order to hear the sounds which are quite faint because of the low value of the current variations which cause the signals. It is highly desirable that the signals received in such a system should be amplified or intensified not only so that they may be more readily heard and heard without the necessity of holding a portion of the receiving apparatus to the ear, but

the other. Preferably the telephone receiver and the microphone are so secured together that a closed chamber is provided between them, the diaphragms of the two instruments belng parallel and opposite to each other on opposite sides of this closed chamber. Because of the fact that the chamber 1s closed, foreign sounds are more effectually excluded and the diaphragm of the mi-- crophone will vibrate in exact correspondence with the vibrations of the diaphragm of the telephone receiver. In order to secure the best results under the variable condltlons lncident to the use of wireless telegraph apparatus, the combined telephone receiver and microphone are so mounted as to permit of varying their angular disposit on. By reason of this provision, it is possible to adjust the microphone to such an angular position as is found by experiment to make it most sensitive under the prevailing conditions. The microphone thus arranged is connected in circuit with a battery and a low resistance telephone receiver so that it controls the current flowing in the circuit of this receiver which latter serves to reproduce the received signals and intensify the sound thereof to such extent that they may be heard distinctly at a substantial distance.

I have illustrated the preferred embodiment of my invention in the accompanying drawings, in which Figure 1 is a front view of the apparatus, broken away in part, with the circuit connections shown diagrammatically, and Fig.

2 is an enlarged sectional view of the pivotally mounted, combined telephone receiver and microphone.

Referring to these drawings, the apparatus is shown as mounted within a rectangular casing 3 on which two binding-posts 4:- are mounted adapted to receive the wires connecting the instrument in the receiving circuit of the system. In Fig. 1 the'receiving circuit of a wireless telegraph system is illustrated diagrammatically, this including an aerial 5 which is connected to the ground through the primary 6 of an oscillation transformer. The secondary 7 of this transformer is connected in circuit with a condenser 8 and the wires :1 and 10 which Patented Aug. 8, i916.

are connee'cted to the binding-posts 4 are connected to opposite sides of the conden er 8.-

"Within the casing 3 is a combined telephone receiver and microphone, these being so mounted as to permit of angular adjustment of their position. The telephone receiver consists of a casing 11 having a diaphragm 12 mounted therein and vibrated by electro-magnets 13 whose coils are connected to binding-posts 14' projecting through the casing 11. These binding-posts are connected by wires 53 -to the bindingposts 4. The casing of the telephone receiver has an opening in the front thereof as shown in Fig. 2 and this opening is in alinement with an opening in the frontpiece 15 of the casing of the microphone. This piece 15 lies against the face of the casing 11 of the telephone and is secured thereto by screws 16. In this way a closed chamber is provided between the diaphragm 12 of the telephone receiver and the diaphragm 17 mounted within the casing of the microphone so that sound waves emanating from sources exterior to the two instruments are practically negligible in their effect upon the diaphragms of the instruments. The back-piece 18 of the casing for the microphone has a carbon block 19 secured thereto by a screw 20 but insulated therefrom by the interposition of suitable insulating material 21. This carbon block has a plurality of cups or depressions formed in one face thereof which face lies very close to the diaphragm 17. These cups or depressions form receptacles in which a pulverulent material 22 such as granular carbon is inserted, each of the depressions being but partially filled by the powdered substance. Onthe piece 18 of the casing of the microphone are two binding-posts, one

of which, indicated at 23, is insulated from the piece 18: This binding-post 23 is con nected by a wire 24 with the carbon block 19. The other binding-post 25 is in electrical connection with the casing of the microphone and hence with the diaphragm 17 thereof. The telephone receiver and microphone thus combined are pivotally mounted so that they may be moved to various angular positions. For this purpose a supporting strip 26 is secured to the casing 11 of the telephone and has trunnions 27 and 28 securedto it in axial alinement. The end of the trunnion 28 is received in a bearing 29 on the casing 3 and the trunnion 27 extends through a bearing in the opposite wall of the casing 3 and has an operating handle 30 secured thereto. This trunnion 27 also has an index 31 secured to it and adapted to move over a scale 32 provided upon the face of the casing 3.

Within the casing 3 is a battery prefer-- ably consisting of a plurality of cells, three cells being shown in the present instance, as indicated at 33, 34 and 35. On the face of the casing is a pivotally mounted switch meagre arm 36 operated by a handle 37 and adapted to contact with any one-of three studs, 3. dead stud 38 and studs 39 and 40, which are connected to the batteries 34 and 33 respectively. The batteries 33 and '34 are 0011- nected together as shown at 41 and the batteries 34 and are connected together as shown at 42.

Two binding-posts 43 and 44 are provided upon the face of the casing, the 0st 43 bein connected to the battery 35 by wire 45 an the post 44 being connected to the binding-post 25 of the microphone by wire 46. The other binding-post 23 of the microphone is connected by wire 47 to the switch arm36.

With the apparatus thus constructed and arranged the variations of current in the receiving circuit of the wireless system vary the magnetic effect of the magnets 13 upon the diaphragm 12 so as to cause vibration of that diaphragm. These vibrations cause corresponding vibrations in the diaphragm 17 of the microphone, which is arranged directly opposite the diaphragm 12 and the vibrations of the diaphragm 17 cause corresponding variations of the resistance of the current paths from the carbon block 19 through the material 22 to the diaphragm 17 These variations of resistance cause corresponding varlations of the current flowing in the circuit from the binding-post 44 to the microphone by wire 46, then to the switch 37 by wire 47 and through the battery to the binding-post 43. These bindingposts 43 and 44 may have a low resistance telephone receiver 48 connected thereto by wires 49, this receiver 48 being preferably provided with a sound amplifier of substantial size. By turning the switch arm 36 so as to contact with either stud 39 or stud 40, either two or three of the cells of the battery may be connected in the circuit of the .microphone and a current strength thus obtained which is found to give the best results. Also the pivotal mounting of the combined telephone receiver and microphone permits of adjusting those parts to the angular position which makes the apparatus most sensitive under the conditions prevailing. When the angular position of fore, sounds which would be very feeble if produced by a telephone receiver inthe circuit of the Wires 9 and lO and which would require that the receiver be held close to the ear, may be amplified so as to permit of hearing-them: quite readily at a substantial distance from the amplifier of the receiver 48. A

- The "apparatus herein described possesses the fu1ther=advantage that it is much more.

sensitiveto urrentfof relatively high frequency-as p. esult -of-iwhich it aids in preventing interference caused by static and other "low. -frequency disturbances.

\ microphone is varied and a battery and a telephone receiver connected in circuit with the microphone, substantially as described. 2. A receiving apparatus comprising the combination of a receiving clrcuit, a telephone receiver connected insaid circuit, a mlcrophone including granular materlal secured to said receiver, means for effecting angular adjustment of the receiver and microphone whereby the degree of conductivity of the microphone is vaiiedeand a battery and a telephone receiver connected in circuit with the microphone, substantially as described. Y

3. A receiving apparatus comprising the combination of a receivingi sci'rcuit," a telephone receiver connected therein; a microphone including granular material, means for securing the receiver"an'd microphone together with their diaphragms opposite each other and a closed chamber between the diaphragms, means for pivotally mounting the combined receiver and microphone :and permitting angular adjustment thereof whereby the degree of conductivity of the microphone is varied and a battery and telephone receiver connected in circuit with the microphone, substantially as described.

In testimony whereof I aifix my signature, in presence of two witnesses.

ALFRED H. GREBE.

Witnesses:

L. BATES, M. A. BILL. 

